Many beverages suffer adverse effects from exposure to oxygen. This is particularly the case with ready-to-drink beverages; especially ready-to-drink coffee beverages. Ready-to-drink coffee beverages are produced by extracting soluble coffee solids from roasted and ground coffee beans using hot water. The extract obtained may then be diluted to a desired concentration, usually to contain about 1% by weight of soluble coffee solids. Various additives are added to the diluted extract which is then filled into containers. The containers are then sealed and subjected to retorting. Certain intermediate steps may also be carried out. For example, the extract may be concentrated and dried to powder prior to formation of the dilute extract. This is usually done when the coffee is filled into the containers at a site different than the site at which the extraction is carried out.
During this process, the coffee may be exposed to oxygen several times. For example, oxygen may be present in the hot water which is used to extract the soluble coffee solids from the roasted and ground coffee beans. Also, the coffee may be exposed to oxygen during extraction or subsequent processing such as concentration and drying. Further, oxygen may get into the container during filling. No matter where in the process the coffee is exposed to oxygen, it is now recognized that the oxygen adversely effects the flavor and aroma of the coffee beverage. In particular, the beverage loses its fresh, clean flavor and aroma; the flavor and aroma which characterizes freshly brewed coffee. Often, bitter, acid flavors develop.
Various measures have been taken in the past to reduce the influence of oxygen. Usually these methods have centered on preventing ingress of oxygen. For example, Japanese patent application 6-141776 discloses extracting coffee grounds using deoxygenated water in an inert gas atmosphere. Further, all subsequent steps, including filling of the dilute extract into containers, is done under inert gas atmosphere. The patent application describes the resulting product to have a good, fresh flavor. The inert gas recommended is nitrogen. The primary problem with this technique is its cost. Carrying out an entire extraction and filling process in a nitrogen gas atmosphere is extremely expensive. Also, deoxygenating water is not a perfect process and not all oxygen is removed.
Another approach which has been attempted is to use antioxidants during the process. For example, U.S. Pat. No. 5,384,143 describes a process in which the coffee extract is rapidly cooled to below 20.degree. C. and then an antioxidant selected from erythorbic acid, ascorbic acid, and their water soluble salts, is added to the cooled extract. The extract is then filled into cans under oxygen free conditions. This technique is less expensive than carrying out the entire process under inert gas atmosphere but there are problems. In particular, coffee is a potent antioxidant which is able to scavenge oxygen faster than most antioxidants commonly used in foods. Therefore, although the antioxidants described in this patent remove some of the oxygen, they are not potent enough to prevent the coffee from scavenging a large portion of the oxygen present. Consequently, the coffee undergoes some oxidative damage.
A further approach has been the use of enzyme systems. For example, the use of systems based upon glucose oxidase and alcohol oxidase have been suggested. However these systems have not proved to be adequate since degradation due to oxygen still occurs. Also, these enzyme systems often produce hydrogen peroxide which is undesirable.
Therefore it is an object of this invention to provide an antioxidant system which is relatively inexpensive and which is sufficiently potent to remove oxygen from beverage components which are themselves antioxidants.